Matched pair analyses of the effect of BMP-7 on osteoarthritis progression. (a) Macroscopic appearances of the femoral condyles at 4, 8, and 12 weeks. To remove individual variability, both sides of the knees of the same individuals are shown. Surface of the cartilage was stained with India ink to identify any fibrillation and erosion. Laterality is shown as lateral (L) and medial (M). Bar = 5 mm. (b) Paired comparison in the macroscopic osteoarthritis score. The scores of the treatment and control knees (in the same animal) are displayed separately and connected with a line (five knees). *P < 0.05, by Wilcoxon's signed rank sum test. (c) Representative histology of femoral condyles. Both sides of the knees from the same individuals are shown. Medial femoral condyles (MFC) and lateral femoral condyles (LFC) were sectioned coronally and stained with safranin-O. Bar = 10 μm. (d) Paired comparison in quantitation of histological analysis using the OARSI cartilage osteoarthritis histopathology grading system (five knees). *P < 0.05 by Wilcoxon's signed rank sum test for paired samples. BMP, bone morphogenetic protein; OARSI, Osteoarthritis Research Society International.